Abstract : Lockheed and Boeing each made a series of tests in aircraft fuel tank simulators to provide an improved understanding of the flowability and pumpability of jet fuels at or below their freezing point where waxy components separate. Each simulator represented a section of an aircraft wing fuel tank. Tests simulated the low temperature cruise environment associated with long duration flights under extreme, high-altitude conditions. Holdup, the fraction of unavailable fuel remaining in the tank after attempted fuel withdrawal, was used to characterize pumpability after low temperature exposure. The test fuels were derived from widely differing crude sources and were selected to cover a range of freezing points. Two of the test fuels were common to the Boeing and Lockheed investigations in order to assess variability due to simulator construction. One fuel in the Lockheed program contained a flow improver additive. In the Boeing program, one fuel was a blend of JP-5 and 9% marine diesel fuel. (Author)